A stamping unit is provided to make all stamping pins stamp uniformly an inner girth side of a conduit even if curvature of the conduit changes by flowing only the stamping pins receiving reaction force inside an upper panel and compacting a spring by the reaction force of the conduit. A stamping unit contains an upper panel(10) having a plurality of perforation holes(11) and a down panel(20) having a plurality of mounting grooves(21) formed corresponding to the perforation hole. The spring(30) is arranged in a mounting groove of the down panel. The spring and the stamping pins(40) are corresponded on a one-to-one basis and the stamping pins are supported by the spring individually. A stamping end part(41) of the stamping pins is protruded through the perforation hole of the upper panel.
